Requirement for a nuclear function of β-catenin in Wnt signaling
Requirement for a nuclear function of β-catenin in Wnt signaling
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DOI：
10.1128/mcb.23.23.8462-8470.2003
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发表时间：
2003-12-01
影响因子：
5.3
通讯作者：
Varmus, H
中科院分区：
文献类型：
--
作者：
Cong, F;Schweizer, L;Varmus, H
Wnt 信号传导可稳定 β-连环蛋白，进而影响 Wnt 反应基因与 T 细胞因子 (TCF) 转录因子的转录。目前，β-连环蛋白的作用有两种模型。传统的核模型表明，β-连环蛋白在细胞核中作用，与 TCF 形成异二聚体转录因子复合物，TCF 提供 DNA 特异性结合，并且 β-连环蛋白的 C 和 N 末端刺激转录。另一种细胞质模型假设 β-连环蛋白从细胞核输出 TCF，以解除其抑制活性或在细胞质中激活它。我们生成了修饰形式的 β-连环蛋白，并使用 RNA 干扰内源性 β-连环蛋白来区分培养的哺乳动物和果蝇细胞中的这些模型。我们发现VP16转录激活结构域可以取代β-连环蛋白的C末端而不丧失功能，并且β-连环蛋白的功能因与组蛋白脱乙酰酶的转录抑制结构域融合而受到损害，有利于β-连环蛋白在细胞核中的直接作用。此外，膜束缚的β-连环蛋白需要与腺瘤性息肉病大肠杆菌蛋白相互作用，但不需要与TCF相互作用才能发挥其功能，而不受束缚的β-连环蛋白需要与TCF结合才能发挥其信号活性。重要的是，通过使用RNA干扰，我们表明膜束缚的β-连环蛋白而不是游离的β-连环蛋白的信号传导活性需要内源性β-连环蛋白的存在，当β-连环蛋白降解机制与膜束缚形式的结合稳定时，内源性β-连环蛋白能够在细胞核中积累。所有这些数据都支持β-连环蛋白正常功能的核模型。
Wnt signaling stabilizes beta-catenin, which in turn influences the transcription of Wnt-responsive genes in conjunction with T-cell factor (TCF) transcription factors. At present, there are two models for the actions of beta-catenin. The conventional nuclear model suggests that beta-catenin acts in the nucleus to form a heterodimeric transcriptional factor complex with TCF, with TCF providing DNA-specific binding and the C and N termini of beta-catenin stimulating transcription. The alternative cytoplasmic model postulates that beta-catenin exports TCF from the nucleus to relieve its repressive activity or activates it in the cytoplasm. We have generated modified forms of beta-catenin and used RNA interference against endogenous beta-catenin to distinguish between these models in cultured mammalian and Drosaphila cells. We show that the VP16 transcriptional activation domain can replace the C terminus of beta-catenin without loss of function and that the function of beta-catenin is compromised by fusion to a transcriptional repressor domain from histone deacetylase, favoring the direct effects of beta-catenin in the nucleus. Furthermore, membrane-tethered beta-catenin requires interaction with the adenomatous polyposis coli protein but not with TCF for its function, whereas untethered beta-catenin requires binding to TCF for its signaling activity. Importantly, by using RNA interference, we show that the signaling activity of membrane-tethered beta-catenin, but not free beta-catenin, requires the presence of endogenous beta-catenin, which is able to accumulate in the nucleus when stabilized by the binding of the beta-catenin degradation machinery to the membrane-tethered form. All of these data support a nuclear model for the normal function of beta-catenin.